A system and method for limiting fixed pattern noise (FPN) in a time delay and integration (TDI) mode of operation of a complementary metal oxide semiconductor (CMOS) imaging device is disclosed. The system and method provide for each line time, selecting a pixel for each column of photosensitive elements in the along track direction to capture dark information such that the selected pixel does not correspond to a portion of a scene that was previously selected to capture dark information in a current TDI period. The dark information for the selected pixels is captured and summed for each column of photosensitive elements. This sum is then used during a next TDI time period to subtract FPN effects from the output of the corresponding column. This allows the dark sum information to be constantly updated while the image sensor is in use while only decreasing the responsitivity by (N−1)/N relative to an N pixel column of a traditional TDI operation.
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1. A method for limiting fixed pattern noise (FPN) in a time delay and integration (TDI) mode of operation of a complementary metal oxide semiconductor (CMOS) imaging device, the method comprising: for each line time, selecting a pixel for each column of photosensitive elements in the along track direction to capture dark information such that the selected pixel does not correspond to a portion of a scene that was previously selected to capture dark information in a current TDI period; for each line time, capturing dark information for the selected pixel to capture FPN effects associated with the selected pixel; summing the dark information captured from each pixel for each column of photosensitive elements over the current TDI period to provide a dark information sum for each column of photosensitive elements; and, correcting TDI pixel output for each column during a next TDI period using the corresponding dark information sum during each line time of the next TDI period.
2. The method of claim 1 , further comprising repeating the selecting, capturing, summing, and correcting steps for each subsequent TDI time period.
3. The method of claim 1 , wherein correcting the TDI pixel output for each column comprises subtracting the corresponding dark information sum during each line time.
4. The method of claim 1 , wherein capturing dark information for the selected pixel comprises preventing transfer of photo-generated charged into a sense node of the selected pixel.
5. The method of claim 1 , wherein the dark information sum is the sum of the dark capture information for each pixel in a column.
6. The method of claim 1 , wherein effective TDI responsivity decreases by (N−1)/N for an N pixel column resulting from the capturing of dark information.
7. The method of claim 1 , wherein correcting TDI pixel output is performed on the same chip as the column of photosensitive elements.
8. The method of claim 1 , wherein correcting TDI pixel output is performed on a different chip as the column of photosensitive elements.
9. A complementary metal oxide semiconductor (CMOS) imaging device operating in a time delay and integration (TDI) mode for limiting fixed pattern noise (FPN), capturing a scene moving with respect to the imaging device, the device comprising: a photosensitive imaging array having at least one column of photosensitive elements; a TDI memory element and addition module for storing and summing output of each photosensitive element for each line time; an FPN memory element and addition module for storing and summing dark information captured from each photosensitive element in the at least one column over a current TDI period to provide a dark information sum for the at least one column of photosensitive elements; and, a dark capture control module for selecting a photosensitive element of the at least one column of photosensitive elements in the along track direction to capture dark information such that the selected photosensitive element does not correspond to a portion of a scene that was previously selected to capture dark information in a current TDI period.
10. The imaging device of claim 9 , further comprising an FPN correction module for correcting TDI output for the at least one column using summed dark information from the FPN memory element stored during the previous TDI period.
11. The imaging device of claim 10 , wherein the FPN correction module is located anywhere of on-chip and off-chip from the photosensitive imaging array.
12. The imaging device of claim 9 , wherein capturing dark information for the selected pixel comprises the dark capture control module preventing transfer of photo-generated charged into a sense node of the selected pixel of the photosensitive imaging array.
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May 9, 2014
August 11, 2015
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